The present invention relates generally to aircraft instrumentation systems. More particularly, the present invention relates to an indicator for displaying the bank angle effective to achieve and maintain a desired rate of turn for an aircraft.
The prior art is replete with various aircraft flight control instruments and displays. These instruments and displays use a combination of alphanumeric and graphical information to indicate the state of the vehicle. The primary flight parameters that are displayed to a pilot are traditionally regarded as being pitch and roll attitude, altitude, airspeed and heading. Secondary parameters may include vertical speed, rate of turn and various navigation and engine related parameters. A number of mechanisms have been devised for presenting this information to the pilot. Early aircraft generally use dedicated instruments for each of these parameters. Modern display technology, however, allows multiple parameters to be presented on a single display. Such flight control displays, which may be of the panel-mounted variety (e.g., heads down display or HDD) or of the heads up display (HUD) variety, are commonly found in commercial, military, and civilian aircraft.
To control an aircraft, a pilot must maintain a high level of awareness of the state of the vehicle and, in particular, the primary flight parameters. To achieve this the pilot must typically continuously and rapidly scan the instrument panel to locate and interpret the displays of the primary flight parameters. The pilot also typically periodically glances at the secondary displays, although this task can be performed at a lower rate than the monitoring of the primary displays. The continual, fast, repetitive scan of the primary flight instruments constitutes a significant workload for the pilot. The difficulty of this task may be compounded by stress and other abnormal or adverse conditions encountered by aircraft operators. When overtaxed, pilots may incorrectly interpret or be confused by even the simplest data and may fail to act, or, conversely, may tend to overreact under the circumstances.
A further common difficulty is that of fixation on a single instrument whose indicated parameter may have excessively varied from a desired value. This type of fixation frequency results in inordinate variation in parameters displayed on other instruments, because of the excessive concentration devoted to the correction of the first-discovered or discrepant parameter.
The workload of the pilot and the probability of pilot error may be mitigated by presenting data to the pilot in a manner that simplifies interpretation and minimizes the effort required to gather the required data.
During instrument flight, certain regulatory authorities, such as the Federal Aviation Administration (FAA), generally direct pilots to perform procedure turns at a standard rate of turn, such as, for example, at a heading change rate of three degrees per second. For some aircraft, the standard rate of turn may be some multiple of this number. For the purposes of this discussion, the FAA standard rate of turn for aircraft, or other appropriate rate of turn, will be referred to as the desired rate of turn of the aircraft. Traditionally, the rate of turn of an aircraft has been displayed on a dedicated scale with markers placed at predefined points, such as, for example, at the xc2x13 degrees per second points on the scale. Such a dedicated scale has been located in a variety of positions on prior art instrumentation panels, such as, for example, on a linear scale below the aircraft attitude indicator and/or on a separate gauge on the instrument panel.
Even though during instrument flight a pilot""s focus must remain on the primary flight instruments while turning, the pilot is also responsible for maintaining the required rate of turn. It is possible for the pilot to maintain a constant rate of turn by maintaining a constant airspeed and roll attitude. To perform a turn, a pilot rolls an aircraft in the direction of the turn to a bank angle approximating the bank angle effective that required to achieve the desired rate of turn. A glance at the rate of turn indicator can then be used to confirm whether the desired rate of turn has been achieved. The roll attitude can then be adjusted to achieve the desired rate of turn. Having achieved the desired rate of turn, the pilot can then complete the maneuver without further reference to the rate of turn indicator by simply maintaining a constant roll attitude and airspeed. This process, however, generally causes the pilot to divert attention away from the primary instruments.
To obtain the initial estimate of the roll attitude (i.e., bank angle) effective to achieve the desired rate of turn of 3 degrees per second, pilots have commonly used a well-known xe2x80x9crule of thumbxe2x80x9d during aircraft operation to calculate this effective bank angle:
xe2x80x83(V÷10)+7
Thus, for example, using this xe2x80x9crule of thumb,xe2x80x9d the pilot of an aircraft flying level (i.e., neither climbing nor descending) at 150 knots would roll the aircraft to a bank angle of 22 degrees to achieve a standard rate of turn of 3 degrees per second.
For a coordinated level turn, the rate of turn is typically a function of the speed of the aircraft and the bank angle as shown in Equation 1:
R.O.T.xe2x88x9dtan(xcex8)/V
where
xcex8=bank angle, degrees
V=Velocity, True Air Speed (TAS)
R.O.T.=Rate of Turn, degrees per second
(See Hurt, H.H. Jr., Aerodynamics for Naval Aviators. US Navy: NAVWEPS 00-80T-80 (1965)).
Given the speed of the aircraft, it is possible to calculate the bank angle effective to achieve a desired rate of turn by solving the above Equation 1 for the bank angle. This gives Equation 2:
xcex8xe2x88x9dtanxe2x88x921(R.O.T.xc3x97V)
FIG. 1 shows a plot of bank angle (xcex8) as a function of airspeed (V) for a number of different desired rates of turn.
A method of integrating display of the bank angle derived from the above equation or other appropriate algorithm relating bank angle to rate of turn with the pilot""s attitude display would allow the pilot to perform a rate turn without diverting attention away from the primary instruments to monitor the rate of turn. A secondary benefit would be the possibility for removal of the standalone rate of turn indicator, thus decreasing cluttering of the instrument panel.
It is, therefore, a general aspect of the instant invention to provide for a single display on which certain critical flight and navigational parameters are simultaneously displayed and to do so in a manner which is intuitively simple for the pilot to use and to interpret, thus enhancing pilot efficiency and safety.
Various embodiments of the present invention provide alternative techniques of displaying aircraft flight information traditionally provided by a standalone rate of turn indicator. The proposed invention not only addresses the problems of space shortage on aircraft display panels, but it also more directly answers a pilot""s question during flight as to what bank angle must be maintained in order to achieve a desired rate of turn at a particular airspeed. Specifically, the proposed invention includes an integral directional marker that is easy to detect and to interpret by the pilot.
In an exemplary embodiment of the present invention, the bank angle effectual to achieve a desired rate of turn is displayed-to the pilot by generating and displaying one or more bank angle markers on the roll scale of the aircraft attitude indicator. The position of the desired rate of turn bank angle markers may be updated continuously as a function of airspeed. The present invention enables a pilot to perform a coordinated turn at the desired rate of turn without having to reference a separate indicator and without having to resort to the traditional xe2x80x9crule of thumb.xe2x80x9d
In a further aspect of one embodiment of the present invention, the desired rate of turn indicator may be designed to compensate for non-level flight and to reflect this in calculating the position of the desired rate of turn bank angle markers. To compensate for non-level flight in calculating the position of the desired rate of turn bank angle markers, it is useful to incorporate factors such as the vertical acceleration of the aircraft into the equation for calculation of the roll angle effective to maintain a desired rate of turn.
The various aspects and embodiments of the present invention described in detail herein assume that the pilot is performing a coordinated turn. Certain aircraft, such as, for example, helicopters, can perform uncoordinated turns, or pedal turns, at low airspeeds. The desired rate of turn bank angle indicator of the present invention may not provide useful information during an uncoordinated turn. Moreover, obtaining accurate airspeed data at very low airspeeds may be difficult due to limitations of some airspeed sensors. In light of these limitations, the desired rate of turn bank angle markers may be removed from the display when the aircraft is traveling at a low airspeed.